This present application relates generally to apparatus, methods and/or systems for improving film cooling of components in gas turbine engines. More specifically, but not by way of limitation, the present application relates to apparatus, methods and/or systems pertaining to film cooling slots with metered flow.
Gas turbine engines typically include a compressor, a combustor, and a turbine. The compressor and turbine generally include rows of blades that are axially stacked in stages. Each stage includes a row of circumferentially-spaced stator blades, which are fixed, and a row of rotor blades, which rotate about a central axis or shaft. In operation, generally, the compressor rotor blades rotate about the shaft, and, acting in concert with the stator blades, compress a flow of air. The supply of compressed air then is used in the combustor to combust a supply of fuel. The resulting flow of hot expanding gases from the combustion is expanded through the turbine section of the engine. The flow of working fluid through the turbine induces the rotor blades to rotate. The rotor blades are connected to a central shaft such that the rotation of the rotor blades rotates the shaft.
In this manner, the energy contained in the fuel is converted into the mechanical energy of the rotating shaft, which, for example, may be used to rotate the rotor blades of the compressor, such that the supply of compressed air needed for combustion is produced, and the coils of a generator, such that electrical power is generated. During operation, because of the high temperatures of the hot-gas path, the velocity of the working fluid, and the rotational velocities found in the compressor and turbine, turbine blades, which, as described, generally include rotor and stator blades, become highly stressed with extreme mechanical and thermal loads.
Often, to reduce the thermal loads, turbine blades are air cooled. Generally, this involves passing a relatively cool supply of compressed air, which is typically bled from the compressor, through internal cooling circuits within the blades. As the compressed air passes through the blade, it convectively cools the airfoil. After passing through the airfoil, the compressed air typically is released through openings on the surface of the blades. When released in a desired manner, the air forms a thin layer or film of relatively cool air at the surface of the airfoil, which both cools and insulates the part from the higher temperatures that surround it. Not surprisingly, this type of cooling is often referred to as “film cooling.” Generally, to adequately cool the blades, numerous film cooling openings, which generally are the outlets of hollow passages that originate at interior cooling cavities, are necessary.
For film cooling to be most effective, it necessary that the air exiting the opening remain entrained in a boundary layer on the surface of the blade for an adequate distance downstream of the opening. However, due to a variety of factors, the effectiveness of conventional film cooling systems decreases rapidly as the distance from the cooling opening increases. While this shortcoming may be cured somewhat by increasing the amount of cooling air released, it is well known in the art that the usage of bypass cooling air should be limited due to its negative impact on efficiency. That is, whenever possible, the use of cooling air should be minimized because such cooling air is working fluid which has been extracted from the compressor and its loss from the gas flow path rapidly reduces engine efficiency. Given these competing factors, conventional film cooling methods either prove moderately ineffective or, when effective, come at a significant cost to the engine efficiency. Prior art advancements that include slots with metered flow, such as, for example, U.S. Pat. No. 4,726,735, improved film cooling performance in certain limited ways, but still fell short of employing the cooling air in an efficient and effective manner. As a result, there remains a need for improved film cooling apparatus, methods and/or systems that minimizes the usage of bypass cooling air.